The specific aims of this study include: evaluating the safety, efficacy, pharmacokinetics, effects on hepatic metabolism and differential effects on postmenopausal symptoms of Estradiol 3-b-glucoside in comparison with oral 17-b-Estradiol. We plan to recruit 30 postmenopausal and post-hysterectomy women who are taking Premarin alone for at least 3 years. They will undergo a four-week wash out period during which Premarin therapy will be stopped. Subjects will then be randomized to receive either 2.0-mg of micronized estradiol or equivalent dose of estradiol-3-b-glucoside daily for 28 days. Laboratory (CBC, coagulation factors, lipids, and liver functions) as well as pharmacokinetic studies (estrone, estradiol and estriol) will be performed at baseline and on day 28. On days 7, 14, 21 blood will also be drawn for estrone, estradiol, and estriol. Our central hypothesis is that daily administration of oral estradiol-3-b-glucoside will produce detectable differences in mean serum levels of estradiol and lower E1/E2 ratios as compared with an equivalent amount of oral micronized estradiol.